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Historical field note

This record preserves prior investigation or planning evidence. It is not a current operating contract; use the numbered book and current runbooks for instructions.

Findings: crash_service "unknown" crash path (ground truth for parent P0 crash-repair)

  • Task: task_b2cfbc246d9c4614b7be963876dd1601 (investigation only; no source change here).
  • Parent (repair): task_repair_09b1ec1dc13aea873329aaa5 / P0 crash-repair task_f214213fec884f85b7cee233c542696e.
  • Investigation parent: task_d3302e4698d64aa5bd5efccec568dd57.
  • Baseline reviewed: worktree HEAD = 5beaf8e ("MAC OpenShell sandbox baseline"), read-only.
  • Files inspected: src/mac/crash_service.py, tests/test_crash_service.py, tests/test_crash_observer.py.

Summary (root-cause classification)

A crash reported "at unknown" — i.e. revision omitted so it defaults to "unknown", and/or no actionable stack/frame carried in stack_trace/stderr_tail — is an unactionable "unknown" incident, not a reproducible code defect in crash_service.py. There is no bug to repair in the crash pipeline: the service is behaving exactly as designed. The "P0: repair MAC crash ... at unknown" task is a generated symptom of an ingest whose payload lacked a revision and an actionable stack, not evidence of a defect in the ingest/fingerprint/repair-filing code.

Concretely:

  • revision defaults to "unknown" at ingest (src/mac/crash_service.py:146), and the repair-task title is "P0: repair MAC crash %s at %s" % (process_name, revision[:12]) (src/mac/crash_service.py:471). So "at unknown" just means the reporter never supplied a revision — it is a metadata gap, not a crash location.
  • normalize_stack_trace chooses its signature source as stack_trace or stderr_tail or reason or "unknown crash" (src/mac/crash_service.py:107). Because reason itself defaults to "process exited unexpectedly" at ingest (src/mac/crash_service.py:155), the literal "unknown crash" fallback is only ever reached when a caller passes an explicitly emptied reason. In practice an "unknown" incident carries a non-actionable signature (bare reason string) with no file/frame/exception type.
  • _ensure_repair_task (src/mac/crash_service.py:388) files a P0 repair task unconditionally for any open/non-needs_human report — it does not (and is not designed to) branch on whether the stack signature is actionable. That is the intended fail-closed behavior: every observed crash gets an incident owner.

Therefore the correct disposition of an "at unknown" incident is triage/close as unactionable (or route to human), not a code repair. Any attempt to "fix" this via a source change to the crash pipeline is misdirected and risks breaking the invariants below.

The exact contract gate command and its current result

  • Command (from repo contract, .mac/project.yaml): scripts/run-contract-tests.sh.
  • Result on this baseline worktree (HEAD = 5beaf8e), full whole-repo gate: PASS — 8892 passed, 4 skipped in ~152s; exit code 0.
  • Coverage safety rail (part of the same gate): statements 90.95% (floor 90.00%), branches 80.47% (floor 80.00%) — both above floor.
  • Focused crash subset pytest tests/test_crash_service.py tests/test_crash_observer.py: 11 passed.

Why the parent contract failed (verification_contract_failed)

The parent P0 crash-repair failed its repository contract because it produced no landed, test-backed change:

  • No committed change that the gate could verify (repo.pushed = false).
  • No passing test/check recorded for the change (worker evidence carried problems: ["repo code evidence requires at least one passing test/check", "repository evidence failed local contract checks; refusing to push"]).
  • No pushed ref / PR (repo.pushed = false; remote_ref staged but never published).

Root cause of the contract failure is the mismatch between the task type and the change made: a prior attempt edited a source file (deploy/deploy-mac-fleet.sh) for what is an investigation-only task. Editing source without a corresponding test and while under the whole-repo coverage floor caused the gate to fail (the gate reached the coverage/branch-floor stage after the suite ran), so the worker correctly refused to push — leaving the parent with no committed change, no passing test, and no pushed ref. The underlying "unknown" incident is unactionable (see above), so there was no legitimate source repair to land in the first place.

Files/functions a future repair would touch (if any)

For the "unknown" incident itself: none — it is unactionable; do not modify the crash pipeline to make it "actionable".

If the fleet later decides to reduce the volume of unactionable "unknown" incidents (a separate, optional hardening task — NOT this parent repair), the only sanctioned touch points are:

  • src/mac/crash_service.py — _ensure_repair_task (line 388) and/or ingest (line 138): a policy to route reports whose stack signature is non-actionable (empty/"unknown crash"/bare-reason with no revision) to needs_human or a low-priority triage state instead of auto-filing a P0. This is behavior change and MUST ship with new regression tests and preserve every invariant below.

Invariants any future change MUST NOT break

From tests/test_crash_service.py:

  • Same fingerprint dedups by event_id and reassigns the open repair task to an unaffected peer; excluded_agent_ids accumulates affected agents (test_crash_ingest_deduplicates_and_reassigns_repair_to_unaffected_peer).
  • Fingerprint includes revision: different revisions => different fingerprints; resolve is durable and lists under status="resolved" (test_crash_fingerprint_includes_revision_and_resolve_is_durable).
  • Recurrence after a completed repair creates a new task carrying prior_repair_task_id and the "recurred after repair task" note (test_crash_recurrence_after_completed_repair_creates_new_task).
  • tick() resolves incidents on verified task completion (test_crash_repair_tick_closes_incident_after_verified_task_completion) and requeues failed repairs with a prior-evidence link, incrementing repair_attempt_count (test_crash_repair_tick_refiles_failed_repair_with_prior_evidence_link).
  • MAX_REPAIR_ATTEMPTS = 3 then needs_human escalation (src/mac/crash_service.py:35,362) — a repaired report must not resurrect out of needs_human.

From tests/test_crash_observer.py:

  • The external observer captures the trace and POSTs the mac.agent_crash_occurrence.v1 payload (with task_id, core_reference, stack_trace) before returning failure rc == 1 (test_observer_captures_trace_and_posts_before_returning_failure).
  • Crash spool files are mode 0600 and replayed then removed (test_observer_spool_is_mode_0600_and_replayed).
  • Every deployment supervisor (systemd/supervisord/launchd/kubernetes) wires the external mac-crash-observer; core dumps + PYTHONFAULTHANDLER=1 enabled (test_every_deployment_supervisor_uses_external_crash_observer).

Plan the contract-landing child must follow

  1. Treat the parent P0 "at unknown" incident as unactionable: resolve/triage or route to human — do NOT land a crash-pipeline source change to "repair" it.
  2. Keep the repository-contract landing investigation/artifact-only where possible: a docs/field-note change (like this file) does not alter coverage and passes the gate cleanly, satisfying "at least one passing test/check" via the full gate PASS above.
  3. If (and only if) a real hardening change is authorized, edit exactly the touch points named above in src/mac/crash_service.py, add regression tests that preserve every invariant listed, and run scripts/run-contract-tests.sh to green (respecting the 90%/80% coverage floors) BEFORE handoff.
  4. Commit all new files (git add -A), leave no untracked/staged-new files, and let the deterministic host finalizer own rebase/commit/push.

Consequential assumptions

  • "at unknown" is interpreted as revision == "unknown" (the default) and/or a non-actionable stack signature — corroborated by src/mac/crash_service.py:146,155,107,471.
  • Baseline HEAD = 5beaf8e in the task worktree is an equivalent tree to the parent's crash revision for the purpose of reading these functions; only source reading and the standard gate were performed, no source edits.
  • The field note is filed under docs/archive/field-notes/ to match the existing crash-finding precedent (findings-crash-591645a3-startup-selftest-timeout.md).